AR Lower Receivers: Cast vs Billet vs Forged Aluminum

Due to its density and ability to resist corrosion; along with it being the most abundant metal in the Earth;s crust, aluminum is used in a multitude of applications across a myriad of industries. Aluminum has become known as a vital component to the aerospace and transportation sectors along with being the ‘go-to’ alloy for manufacturing AR-15 uppers and AR lower receivers.

1. Cast Aluminum AR Lower Receiver

One of the processes for manufacturing an AR-15 lower receiver is to ‘cast’ the lower. This means the lower receiver is formed using a mold. Molten aluminum is poured into the mold to form the overall shape of the lower. Once the aluminum solidifies the aluminum ‘casting’ is removed from the mold. The ‘cast’ lower receiver is then finished on a CNC machine.

Cast lower receivers offer buyers some of the most economical lowers of the three manufacturing processes. Furthermore, by casting a lower receiver from A380 aluminum the lower is given the best synthesis of mechanical properties offered by a casting process.

Cast receivers are also the blunt of unfair criticism. Due to a handful of manufacturers who became known for poor casting and inattention to detail, the cast lower has received a bad rap. Although, if properly cast and heat treated, a cast lower receiver can be suitable for most AR-15 applications.

2. Billet Aluminum AR Lower Receiver

A billet lower receiver is formed from a solid block of aluminum often called ‘bar stock.’ This ‘bar stock’ is formed from extruded aluminum. “Extruded” simply means the aluminum was formed into a particular shape by rolling between two rollers. (A mental image might be to think of it as a piece of dough, which was extruded or ‘rolled’ and cut to various shapes to form different types of pasta.) From a piece of this extrusion or ‘bar stock’ a CNC machine will cut the billet into the shape of an AR-15 lower receiver.

Due to the CNC’s ability to machine billet aluminum into designated shapes, billet lower receivers are considered the most aesthetic. While one-piece trigger guards, fine lines and geometric designs do little for overall performance, some AR builders consider these to be bonus features when considering the overall look of their AR build.

3. Forged Aluminum AR Lower Receiver

Forged aluminum generally refers to material that is ‘forged’ into a specified shape. Forging a lower receiver requires “compressive forces.” In other words it is “hammered” into forging dies to shape the aluminum into the intermediate dimension of the lower receiver. After the aluminum lower is forged into the initial shape, the raw forging is then ‘finished’ on a CNC machine.

Metallurgists agree that a forged piece of aluminum is stronger than cast or billet. The reason being, when the material is shaped under pressure, its ‘grain’ follows the same shape as the part. As a result, the product manufactured is stronger due to the continuous grain characteristics allowed by the forging process.

Summary

Although personal preference will ultimately be the deciding factor as to what lower receiver you purchase, each method of manufacturing offers some form of benefit. While there has been great debate between the loyalists of each manufacturing process, few can attest to the failure of any lower that has been purchased from a quality manufacturer.